Prior art interactive buffered raster displays include low persistance phosphor multiple gun color cathode ray tubes (CRTs). Such a CRT is the electronic medium upon which an image is painted by way of electron beam deflection and intensity modulation of its multiple color guns. Information, both defining the image to be painted and providing the necessary control, is obtained from a buffer intermediate the CRT display and a stored program controlled processor. The processor executes lists of graphical orders ultimately resulting in the CRT painted image. Among its tasks, the processor performs vector-to-raster conversion and causes bit values in the form of a multibit code to be stored in a counterpart location in the buffer. The multibit code, termed a "pixel", consists of an x,y position coordinate and a color number or value. As each pixel is extracted from the display buffer during a horizontal scan of a raster driven display, the bits are used to index a translate table which converts them into a larger number of bits. This larger number of bits, in turn, drives designated red, green and blue digital-to-analog converters actually modulating the multi-gun CRT beam intensities. Illustration may be found in Langdon, et al U.S. Pat. No. 4,255,861, issued Sept. 30, 1980. In this art, the purpose of the translate table is to minimize display refresh buffer size while maximizing the number of distinct displayable colors.
The display or graphic order list executed by the processor may consist of long instruction strings. At this level, editing of such strings involves reprocessing of the entire image and is considered computationally intense. For example, in prior art vector graphic systems, an editing function involving the correlation between display position coordinates of any light pen interrupt and the identity of a graphical object in the immediate vicinity requires rescanning of the display order list with multitudinous object/light pen position comparisons. Even a moderately complex display of 100 objects might require several hundred thousand orders with a significant number of comparisons. Although in correlation and echoing it was known to use a side file for reducing the computation by retaining the position coordinates of objects in a sorted order, this nevertheless still mandated a binary search for ascertaining the object identity given the light pen interrupt position. Relatedly, associative memories were used in the early 1970's in which position indexing of object identity was known. However, the several higher orders of magnitude cost of associative memory relative to RAM greatly diminished interest.
Stillman, 20 CACM, pp 331-339, May 1977; Newman, et al, "Principles of Interactive Computer Graphics", Second Edition, McGraw Hill, 1979 at pages 217-245 and 247-289; and Foley, "Fundamentals of Interactive Computer Graphics", Addison Wesley, 1982, at pages 123-136, 466-475 and 497-503, describe a raster graphic system responsive to a light pen interrupt which erases the display buffer and then reconstructs the image from an order list. Correlation is registered when the object being drawn by the execution of the order list had the same coordinates as the light pen position. Furthermore, these references describe dynamically changing color translation maps to achieve animation. Thus, the art teaches that because buffered raster displays do not dynamically process an order list but rather refresh the display from the stored raster image of a reprocessed order list, then editing must be performed at the display processor level.